The prior art teaches front-end corner modules for motor vehicles in which a knuckle is attached to a vehicle chassis as by several links, such that the knuckle is pivoted relative to the chassis by a steering rod coupling the knuckle to the vehicle's steering system. Typically, a bearing on the knuckle supports a half shaft or stub shaft for relative rotation. The shaft, in turn, supports a wheelend assembly that typically includes a wheel hub mounted on the shaft, a rotor having a center portion mounted on the wheel hub, and a wheel and tire combination mounted on the wheel hub as by a plurality of lug bolts.
In order to facilitate repair and replacement of the wheelend's several components, the wheel hub is typically removably mounted on a splined section of the shaft and axially secured by a nut threadably mounted on the threaded outboard end of the shaft. The splined section of the shaft is typically formed by rolling the spine in the end of the shaft and then heat treating the rolled spline for strength and toughness. A slight helix or twist is often added to the spline along its entire length to minimize backlash upon tightening of the nut to secure the wheel hub on the outboard end of the shaft.
Unfortunately, the post-rolling heat treatment of the shaft introduces dimensional variations in the splined portion of the shaft. To accommodate tolerance accumulation, the prior art has resorted to use of relatively longer lengths of splined engagement between the wheel hub and the shaft. Such increased axial length of engagement between wheel hub and shaft, in turn, generates a larger scrub radius, for a given wheel-and-tire combination having a fixed offset. Moreover, the tolerance variations in the splined portion of the shaft combine with hub, rotor, and bearing tolerance stack-ups to increase run-out, particularly as to the friction ring of the brake rotor, and to reduced shaft-wheel hub concentricity, thereby limiting possible improvements to vehicle Noise, Vibration and Harshness (NVH) levels.
Alternatively, U.S. Pat. No. 6,450,585 teaches a wheelend assembly featuring a polygonal shaft-wheel hub interface, wherein the helical spline is replaced by a tapered end portion of the shaft featuring a polygonal outer contour defining a plurality of machined lobes. By using a taper to provide a slightly conical construction of the polygonal outer contour, the '585 patent teaches that a shaft-hub interface is achieved which is free of play in both the axial and radial directions.
However, as in the case with known splined interfaces, the tapered polygonal shaft-wheel hub interface requires a significantly increased length of axial engagement of the shaft-wheel hub interface, exceeding perhaps 65% or more of the maximum diameter of a given lobe, particularly as the number of lobes is reduced to a number approaching a minimum number of three lobes. This increased length of axial engagement of the shaft-wheel hub interface, in turn, tends to increase scrub radius or kingpin offset for a given wheel-tire combination used with the wheelend assembly, thereby limiting design and packaging flexibility when using such a shaft-hub interface. Moreover, the increased-axial-length, tapered shaft-wheel hub interface requires particularly tight tolerances in order to ensure that the inboard face of the wheel hub can still be suitably biased against the bearing's inner race by a threaded fastener on the outboard end of the shaft, with an attendant increase in manufacturing costs, in order to avoid an unintended increase in wheel hub runout.
Accordingly, what is needed is an improved wheelend assembly featuring a shaft-wheel hub interface that overcomes the aforesaid deficiencies of the prior art.